Question: why cant we have injections to stop us getting all cancers like we did with cervical cancer?

The reason that an injection exists for vaccination against cervical cancer, is that it can be caused by a virus: the HPV virus. Considering that not all cancers are caused by viruses in this way, it is not possible to generate (at least, not yet, and not in the same way as the cervical cancer jab) vaccines for all other cancers.